The field of this invention relates to the recovery of cesium from cesium-bearing minerals such as pollucite. More specifically, this invention relates to an improvement in such recovery processes wherein the cesium ore is extracted with a strong mineral acid to obtain an extract of the acid salts for further processing.
Processes for the recovery of cesium from pollucite and other cesium-containing minerals were reviewed by J. J. Kennedy in Chemical Reviews, Vol. 23 (1938), Pages 157-163. More recent technical developments were summarized by R. A. Heindl, Bureau of Mines Bulletin 650, "Mineral Facts and Problems" (1970 ed.), pages 527-534. In one process which has undergone considerable development for commercial use, ground pollucite ore is leached with strong sulfuric acid to obtain an extract containing cesium alum, which is recovered by crystallization for further processing. The cesium alum process has been considered a traditional process for recovering cesium from pollucite. However, other recovery processes have been proposed as described in the above citations. The first step of most such processes is an acid leaching of the pollucite to obtain cesium as a soluble salt in admixture with other metal salts. Such acid extraction occurs readily with a variety of strong acids, including not only sulfuric acid but also hydrobromic and hydrochloric acids.
Since pollucite ore contains substantial amounts of other alkali metals besides cesium such as rubidium, and potassium or sodium, as well as substantial amounts of polyvalent metals, primarily aluminum but also iron, acid leaching results in an extract containing the soluble cesium salt in admixture with other alkali metal and polyvalent metal salts. The efficient recovery of the cesium values from such extracts has therefore presented the art with a difficult problem, since it is desired to obtain the recovered cesium compound in as pure a form as possible for further processing to commercial cesium products, such as cesium chloride, cesium iodide, cesium carbonate, cesium sulfate, and also metallic cesium.
As already mentioned, where sulfuric acid is used for the digestion step, the cesium can be recovered as cesium alum, expressed as CsAl(SO.sub.4).sub.2.12H.sub.2 O or Cs.sub.2 SO.sub.4.Al.sub.2 (SO.sub.4).sub.3.24H.sub.2 O. Where hydrobromic acid is used, the aluminum bromide can be removed first by isopropyl alcohol extraction, and the mixed alkali metal bromides recovered and treated in an extractor to obtain a solution of cesium tribromide, which upon evaporation yields cesium bromide.
Where hydrochloric acid is the extractant, it has been proposed to selectively precipitate the cesium by addition of antimony chloride to form a precipitate of cesium antimony chloride (CsSbCl.sub.6), which can be separated and decomposed in water to cesium chloride and a water-soluble compound of antimony. The cesium chloride can then be reacted with perchloric acid to produce crystals of cesium perchlorate, which can be recovered, and then decomposed to obtain cesium chloride as the final product. See U.S. Pat. No. 2,808,313 (1957).
While the above described processes are capable of producing cesium sulfate, cesium bromide, and cesium chloride in relatively high purity, these processes have proven to be difficult and expensive for commercial application. Therefore, there has been a recognized need for an improved process for recovering cesium from pollucite in a highly purified form. The need for such a process improvement has been emphasized in recent years by the increasing uses of cesium and cesium compounds, and by the projected expansion of these uses in anticipated applications. (See Heindl, above cited, pages 528-532.)